Code:
' Invokes either the spell or grammar checker. 
Private Sub SpellOrGrammarCheck(ByVal blnSpellOnly As Boolean)

Try
' Create Word and temporary document objects.
Dim objWord As Word.Application
Dim objTempDoc As Object
' Declare an IDataObject to hold the data returned from the clipboard.
Dim iData As IDataObject

' If there is no data to spell check, then exit sub here.
If Me.Text = "" Then
Exit Sub
End If

objWord = New Word.Application

objTempDoc = objWord.Documents.Add
objWord.Visible = False

' Position Word off the screen...this keeps Word invisible throughout.
objWord.Visible = False
objWord.WindowState = 0
objWord.Top = -3000

' Copy the contents of the textbox to the clipboard
Clipboard.SetDataObject(Me.Text)

' With the temporary document, perform either a spell check or a complete
' grammar check, based on user selection.
With objTempDoc
.Content.Paste()
.Activate()
If blnSpellOnly Then
.CheckSpelling()
Else
.CheckGrammar()
End If
' After user has made changes, use the clipboard to
' transfer the contents back to the text box
.Content.Copy()
iData = Clipboard.GetDataObject
If iData.GetDataPresent(DataFormats.Text) Then
Me.Text = CType(iData.GetData(DataFormats.Text), String)
End If
.Saved = True
objWord.Visible = False
.Close()
End With

objWord.Quit()

MessageBox.Show("The spelling check is complete.", "Spell Checker", MessageBoxButtons.OK, MessageBoxIcon.Information)

' Microsoft Word must be installed. 
Catch COMExcep As COMException
MessageBox.Show("Microsoft Word must be installed for Spell/Grammer Check to run.", "Spell Checker")

Catch Excep As Exception
MessageBox.Show("An error has occured.", "Spell Checker")

End Try

End Sub
Here's the code that I use to make a spell on textBox in my VB application. It works fin but now I want to specify the language to use.

An idea ? Thx